Answer:

D2
|
|
no 
no i
no Sn
|

D2 (reflected)
|
|
The mirror image of the
D2 diagram is
nonsuperposable to
the original diagram.
|
Problems such as this one demonstrate the value of point group diagrams.
Imagine you had to check the chirality or not so of a D2
molecule manually (e.g. twistane or C76 (D2)).
|